#define _CRT_SECURE_NO_WARNINGS 0
#include <stdio.h>
int main(){
	int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
	int sz = sizeof(arr) / sizeof(int);
	int left = 0;
	int right = sz - 1;
	int n = 0;
	scanf("%d", &n);

	while (left<=right) {
		int mid = (left + right) / 2;
		if (arr[mid] > n) {
			right = mid - 1;
		}
		else if (arr[mid] < n) {
			left = mid + 1;
		}
		else
			printf("找到：%d", mid);
			break;
		}
	}
	if (left > right) {
		printf("找不到此数");
	}
}